Light emitting device

ABSTRACT

The present disclosure provides a light-emitting device, comprising: a light-emitting stack; a first semiconductor layer on the light-emitting stack; a first electrode formed on the first semiconductor layer and comprising an inner segment, an outer segment, and a plurality of extending segments electrically connecting the inner segment with the outer segment.

REFERENCE TO RELATED APPLICATION

This application is a continuation application of a previously filedU.S. patent application Ser. No. 15/410,441 filed on Jan. 19, 2017,entitled as “LIGHT EMITTING DEVICE”, which is a continuation-in-part ofa previously filed U.S. patent application Ser. No. 14/949,414 filed onNov. 23, 2015, entitled as “LIGHT EMITTING DEVICE”, which claims theright of priority based on U.S. provisional application Ser. No.61/802,792, filed on Mar. 18, 2013, and the right of priority based onTW application Serial No. 102127373, filed on Jul. 30, 2013. The entirecontents of each of these applications are hereby incorporated byreference.

BACKGROUND Technical Field

The present disclosure relates to a light-emitting device, and inparticular to a light-emitting device comprising a light-absorbinglayer.

Description of the Related Art

The light-emitting diodes (LEDs) of the solid-state lighting elementshave the characteristics of low power consumption, low heat generation,long operational life, shockproof, small volume, quick response and goodopto-electrical property like light emission with a stable wavelength sothe LEDs have been widely used in household appliances, indicator lightof instruments, and opto-electrical products, etc.

A light-emitting diode usually comprises a light-emitting stack and twoelectrodes provided for injecting a current into the light-emittingstack for emit light. In general, two electrodes are design to have acurrent spreading throughout the light-emitting stack such that alight-emitting area configured to emit light is substantially the sameas the surface area of the light-emitting stack. However, in otherapplication, there is a need for a light-emitting having a limitedlight-emitting area with a high current density for improving lightefficiency thereat.

SUMMARY OF THE DISCLOSURE

The present disclosure provides a light-emitting device.

The light-emitting device comprises: a light-emitting stack; a firstsemiconductor layer on the light-emitting stack; a first electrodeformed on the first semiconductor layer and comprising an inner segment,an outer segment, and a plurality of extending segments electricallyconnecting the inner segment with the outer segment.

BRIEF DESCRIPTION OF THE DRAWING

The accompanying drawing is included to provide easy understanding ofthe application, and is incorporated herein and constitutes a part ofthis specification. The drawing illustrates the embodiment of theapplication and, together with the description, serves to illustrate theprinciples of the application.

FIG. 1 shows a top view of a light-emitting device in accordance withthe first embodiment of the present disclosure.

FIG. 2 shows a cross-sectional view of the light-emitting device, takenalong line AA′ of FIG. 1.

FIG. 3 shows a top view of a light-emitting device in accordance withthe second embodiment of the present disclosure.

FIG. 4 shows a cross-sectional view of the light-emitting device, takenalong line BB′ of FIG. 3.

FIG. 5A shows a top view of a light-emitting device in accordance withthe third embodiment of the present disclosure.

FIG. 5B shows a cross-sectional view of the light-emitting device, takenalong line XX′ of FIG. 5A.

FIG. 6 shows a top view of a light-emitting device in accordance withthe third embodiment of the present disclosure.

FIG. 7 shows a top view of a light-emitting device in accordance withthe third embodiment of the present disclosure.

FIG. 8 shows a top view of a light-emitting device in accordance withthe fourth embodiment of the present disclosure.

FIG. 9 is a cross-sectional view along an A-A′ line shown in FIG. 8after a step of roughing.

FIG. 10 is a cross-sectional view along an A-A′ line shown in FIG. 8before the step of roughing.

FIG. 11 is a cross-sectional view along a B-B′ line shown in FIG. 8.

FIG. 12 disclose a light-emitting device 500 in accordance with thefifth embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

To better and concisely explain the disclosure, the same name or thesame reference number given or appeared in different paragraphs orfigures along the specification should has the same or equivalentmeanings while it is once defined anywhere of the disclosure.

The following shows the description of embodiments of the presentdisclosure in accordance with the drawing.

FIGS. 1 and 2 disclose a light-emitting device 100 in accordance withthe first embodiment of the present disclosure. FIG. 1 shows the topview of the light-emitting device 100 and FIG. 2 shows thecross-sectional view of the light-emitting device 100. Thelight-emitting device 100 comprises a substrate 10, a light-emittingstack 13 formed on the substrate 10, a reflective layer 12 formedbetween the substrate 10 and the light-emitting stack 13, and a bondinglayer 11 formed between the reflective layer 12 and the substrate 10.The light-emitting stack 13 comprises a first-type conductivitysemiconductor layer 131, a second-type conductivity semiconductor layer133, and an active layer 132 sandwiched between the first-type andsecond-type conductivity semiconductor layers 131, 133. The first-typeand second-type conductivity semiconductor layers 131, 133 respectivelyprovide electrons and holes such that electrons and holes can becombined in the active layer 132 to emit light when a current is appliedthereto. The material of the light-emitting stack 13 comprises III-Vgroup semiconductor material, such as Al_(x)In_(y)Ga_((1-x-y))N orAl_(x)In_(y)Ga_((1-x-y))P, wherein 0≦x, y≦1; (x+y)≦1. Depending on thematerial of the active layer 132, the light-emitting stack 13 is capableof emitting a red light with a wavelength in a range from 610 nm to 650nm, a green light with a wavelength in a range from 530 nm to 570 nm, ablue light with a wavelength in a range from 450 nm to 490 nm or a UVlight with a wavelength in a range from 400 nm-450 nm. A method ofmaking the light-emitting stack 13 is not limited to but comprisesMetal-organic Chemical Vapor Deposition (MOCVD), Molecular Beam Epitaxy(MBE), Hydride Vapor Phase Epitaxy (HVPE), evaporation or ionelectroplating. The light-emitting device 100 further comprises a firstelectrode 16 formed on the second-type conductivity semiconductor layer133, a second electrode 17 formed on the substrate 10, a light-absorbinglayer 18 formed on a portion of the first electrode 16, and aninsulation layer 19 formed between the light-absorbing layer 18 and thesecond-type conductivity semiconductor layer 133. In this embodiment,the first electrode 16 is patterned and comprises an inner segment 161,an outer segment 162, and a plurality of extending segments 163electrically connected the inner segment 161 with the outer segment 162.As shown in FIG. 2, the light-emitting device 100 further comprises anohmic contact layer 15 formed between the inner segment 161 and thelight-emitting stack 13 for providing an ohmic contact paththerebetween. The ohmic contact layer 15 has a shape substantially equalto that of the inner segment 161. The ohmic contact layer 15 is notformed between the outer segment 162 and the light-emitting stack 13.Alternatively, the ohmic contact layer 15 can be formed between theouter segment 162 and the light-emitting stack 13, and has a shapesubstantially equal to that of the outer segment 162 (not shown). Theinner segment 161 and the outer segment 162 comprise a circle,rectangle, quadrangle or polygon in shape. When the inner segment 161and the outer segment 162 are a circle in shape, they are concentric.

Referring to FIG. 2, the second-type conductivity semiconductor layer133 of the light-emitting stack 13 has a side wall 1331 and a topsurface. The top surface has a first region 1332 and a second region1333. The second region 1333 is defined by the outer segment 162 formedon the first region 1332 such that the first region 1332 surrounds thesecond region 1333. Specifically, the outer segment of the first region1332 surrounds the second region 1333. The inner segment 161 is formedon a portion of the second region 1333 without covering the entiresecond region 1333 so a partial second-type conductivity semiconductorlayer 133 is exposed for the light emitted from the active layer 132 topass outside the light-emitting device 100 therethrough. The exposedsecond region 1333 where there is no inner segment 161 disposed can beroughed by etching such as dry etching or wetting etching for improvinglight extraction. The light-absorbing layer 18 has a first portion 181surrounding the side wall 1331 and a second portion 182 above the firstregion 1332 of the top surface of the light-emitting stack 13.Specifically, the insulation layer 19 and the outer segment 162 isformed on and covering the first region 1332 of the top surface of thesecond-type conductivity semiconductor layer 133 and the second portion182 of the light-absorbing layer 18 is formed on and covering theinsulation layer 19 and the outer segment 162. In addition, theinsulation layer 19 covers the side wall 1331 of the light-emittingstack 13 and the first portion 181 covers a side wall of the insulationlayer 19. Since the ohmic contact layer 15 is merely formed between theinner segment 161 and the light-emitting stack 13, the active layer 132below the inner segment 161 (that is, the second region) emits lightsuch that a first quantity of the light (more than 90%) directly passesoutside the light-emitting device 100 through the second region 1333 anda second quantity of the light (less than 10%) may emit toward thelight-absorbing layer 18 which is configured to absorb light. In oneembodiment, more than 50% of the second quantity of the light isabsorbed by the light-absorbing layer 18. In addition, the light emittedfrom the active layer 132 does not pass outside the light-emittingdevice 100 through the first region 1332 and the side wall 1331. A ratioof an area of the second region 1333 to an area of the top surface ofthe light-emitting stack 13 is between 10%-90%, that is, alight-emitting area is defined as 10%-90% of the area of thelight-emitting stack 13. The light-absorbing layer 18 can comprise asingle layer or a plurality of sublayers and has a thickness larger than300 Å. The light-absorbing layer 18 comprises titanium (Ti), chromium(Cr), nickel (Ni), Au, or combinations thereof. The first electrode 16comprises metal or metal alloy. The metal comprises Cu, Al, Au, La, orAg. The metal alloy comprises La, Ge—Au, Be—Au, Cr—Au, Ag—Ti, Cu—Sn,Cu—Zn, Cu—Cd, Sn—Pb—Sb, Sn—Pb—Zn, Ni—Sn, or Ni—Co. The light-absorbinglayer 18 can comprise a bonding pad for wire bonding to an externalstructure (not shown), for example, a submount, and therefore forming anelectrical connection therebetween when in operation.

In this embodiment, the reflective layer 12 is embedded within thebonding layer 11 in a position corresponding to the second region 1333of the top surface of the light-emitting stack 13. Accordingly, when thelight emitted from the active layer 132 emits toward the substrate 10,the light can be reflected by the reflective layer in opposite directiontoward the second-type conductivity semiconductor layer 133. Since someof the light only passes outside through the second region 1333 of thetop surface of the second-type conductivity semiconductor layer 133, thereflective layer 12 has an area substantially equal to that of thesecond region 1333 of the top surface of the light-emitting stack 13. Inother embodiment, the reflective layer 12 can have an area substantiallylarger than that of the second region 1333 of the top surface of thelight-emitting stack 13.

FIGS. 3 and 4 disclose a light-emitting device 200 in accordance withthe second embodiment of the present disclosure. FIG. 3 shows the topview of the light-emitting device 200 and FIG. 4 shows thecross-sectional view of the light-emitting device 200. Thelight-emitting device 200 has the similar structure with the firstembodiment of the light-emitting device 100 except that the innersegment 161 has two inner sub-segments 1611, 1612. A plurality of firstextending segment 1631 electrically connects the two inner sub-segments1611, 1612 with the outer segment 162 and a plurality of secondextending segments 1632 electrically connects one of the two innersub-segments 1611, 1612 with the outer segment 162. The first extendingsegment 1631 and the second extending segments 1632 are alternatelyarranged. The outer segment 162 comprises a plurality of protrusions164. The outer segment 162 and the protrusions 164 are provided fordefining the second region 1333 where the light emitted from the activelayer 132 merely passes outside the light-emitting device 200therethrough. As shown in FIG. 4, the ohmic contact layer 15 is formedbetween the two inner sub-segments 1611, 1612 and the light-emittingstack 13 for providing an ohmic contact path therebetween. The ohmiccontact layer 15 has a shape substantially same as that of the two innersub-segments 1611, 1612 of the inner segment 161. The ohmic contactlayer 15 is not formed between the outer segment 162 and thelight-emitting stack 13. Alternatively, the ohmic contact layer 15 canbe formed between the outer segment 162 and the light-emitting stack 13,and has a shape substantially same as that of the outer segment 162. Theinner two sub-segments 1611, 1612 of the inner segment 161 and the outersegment 162 comprise a circle, rectangle, quadrangle or polygon inshape. When the two inner sub-segments 1611, 1612 of the inner segment161 and the outer segment 162 are a circle in shape, they areconcentric. A ratio of an area of the second region 1333 to an area ofthe top surface of the light-emitting stack 13 is between 10%-90%. It isnoted that numbers of the inner segment and the outer segments can bevaried depending on the actual requirements. The larger the desired areaof the second region where the light emitted from the active layerpasses outside the light-emitting device therethrough, the more numbersof the inner segment and the outer segments are.

FIGS. 5A and 5B disclose a light-emitting device 300 in accordance withthe third embodiment of the present disclosure. FIG. 5A is a top view ofthe third embodiment. FIG. 5A shows a cross-sectional view of thelight-emitting device, taken along line XX′ of FIG. 5A. As shown in FIG.5A, the light-emitting device 300 comprises a light-emitting area and anelectrode area surrounding the light-emitting area. The light-emittingarea is substantially arranged in a center of the light-emitting device300. The electrode area is a light-absorbing area, or anon-light-emitting area. The light-emitting area has a shape of circlein top view. It is noted that the shape is not limited and can bepolygon, such as triangle or square. Assuming the shape of thelight-emitting area is a circle, its diameter is between 0.004-0.5 mm.In one embodiment, the diameter is between 0.001-0.2 mm. Thelight-emitting device 300 has a structure similar to the light-emittingdevice 100 of the first embodiment, except that the light-emittingdevice 300 comprises a trench 20 for separating an epitaxial structure33 into a first semiconductor structure 22 and a second semiconductorstructure 24. The first semiconductor structure 22 has a shape of circlein top view and the second semiconductor structure 24 surrounds thefirst semiconductor structure 22. The first semiconductor structure 22and the second semiconductor structure 24 have substantially the sameepitaxial structure 33 and have the same material composition and thesame stacking structure. The epitaxial structure 33 comprises afirst-type conductivity semiconductor layer 331, a second-typeconductivity semiconductor layer 333, and an active layer 332 disposedbetween the first-type conductivity semiconductor layer 331 and asecond-type conductivity semiconductor layer 333. The trench 20separates the active layer 332 and the second-type conductivitysemiconductor layer 333 of the first semiconductor structure 22 from theactive layer 332 and the second-type conductivity semiconductor layer333 of the second semiconductor structure 24. However, the first-typeconductivity semiconductor layer 331 of the first semiconductorstructure 22 and the first-type conductivity semiconductor layer 331 ofthe second semiconductor structure 24 are physically connected with eachother. When the first semiconductor structure 22 is driven by a current,the active layer 332 of the first semiconductor structure 22 can emit afirst light with a first main wavelength; and when the secondsemiconductor structure 24 is driven by a current, the active layer 332of the second semiconductor structure 24 can emit a second light with asecond main wavelength. The first main wavelength and the second mainwavelength are within the same wavelength range. The first mainwavelength and the second main wavelength have the same wavelength, forexample, a red light having a wavelength of 610 nm-650 nm, a green lighthaving a wavelength of 530 nm-570 nm, or a blue light having awavelength of 450 nm-490 nm. In another embodiment, the first mainwavelength can be different from the second main wavelength.

In order to avoid the first light from the active layer 332 of the firstsemiconductor structure 22 being emitted toward the second semiconductorstructure 24, the trench 20 comprises one or more insulation layer. Theinsulation layer comprises an insulation material for absorbing thefirst light or reflecting the first light. The insulation materialcomprises an organic polymer material or inorganic material.

A reflective layer 12 of the light-emitting device 300 overlayingportions of the first semiconductor structure 22 is physically connectedwith the reflective layer 12 overlaying portions of second semiconductorstructure 24. In a top view, the reflective layer 12 is configured toarrange at a position corresponding to the light-emitting area, and thereflective layer 12 has an area substantially equal to or larger thanthat of the light-emitting area. When the first light and/or the secondlight from the active layer 332 emits toward the substrate 10, the firstlight and/or the second light can be reflected toward the second-typeconductivity semiconductor layer 333 and escape outward at a side nearto the second-type conductivity semiconductor layer 333. Specifically,all the first light and/or the second light substantially emit outwardfrom a top surface 33S of the light-emitting device 300. In oneembodiment, the top surface 33S comprises a rough surface formed byetching or imprinting for improving the light extraction of thelight-emitting device 300.

As shown in FIG. 5A, the electrode area comprises a plurality ofexternal electrode structure. The plurality of external electrodestructure substantially surrounds the second semiconductor structure 24and comprises a first external electrode structure 28 and a secondexternal electrode structure 38. Each of the first external electrodestructure 28 and the second external electrode structure 38 can be abonding pad for wire bonding to an external structure (not shown), forexample, a submount, and therefore forming an electrical connectiontherebetween when driven by a current. The first external electrodestructure 28 and a second external electrode structure 38 respectivelycomprise an insulation layer 19 and a conductive layer 281. Theinsulation layer 19 is disposed between the second semiconductorstructure 24 and the conductive layer 281. A material of the conductivelayer 281 comprises metal or metal alloy. The metal comprises La, Cu,Al, Au, or Ag. The metal alloy comprises GeAu, BeAu, CrAu, AgTi, CuSn,CuZn, CuCd, Sn—Pb—Sb, Sn—Pb—Zn, NiSn, or NiCo.

As shown in FIG. 5A, there are a pair of the first external electrodestructure 28 and a pair of the second external electrode structure 38.The pair of the first external electrode structure 28 is disposed atopposite positions and facing each other and the pair of the secondexternal electrode structure 38 is disposed at opposite positions andfacing each other. In this embodiment, the first external electrodestructure 28 and the second external electrode structure 38 arealternately arranged. In other embodiment, a number and an arrangementof the first external electrode structure 28 and the second externalelectrode structure 38 can be varied but not be limited to abovedescription.

As shown in FIGS. 5A and 5B, the light-emitting device 300 comprises aplurality of extension electrode on the epitaxial structure 33.Specifically, the plurality of extension electrode comprises a firstextension electrode 221 disposed on the first semiconductor structure 22and a second extension electrode 241 disposed on the secondsemiconductor structure 24. The first extension electrode 221 or thesecond extension electrode 241 comprises a circular shape. However, anumber and a shape of the first extension electrode 221 and the secondextension electrode 241 can be designed to enhance current spreading.

As shown in FIG. 5A, the light-emitting device 300 comprises a firstconnecting electrode 223 connecting the first extension electrode 221 tothe first external structure 28, and a second connecting electrode 243connecting the second extension electrode 241 to the second externalstructure 38.

In one embodiment, the light-emitting device 300 can comprise an ohmiccontact layer at a position corresponding to the extension electrode,for example among the first extension electrode 221, the secondextension electrode 241 and the epitaxial structure 33. As shown in FIG.5B, the light-emitting device 300 comprises a first ohmic contact layer222 disposed between the first extension electrode 221 and thesecond-type conductivity semiconductor layer 333, and a second ohmiccontact layer 242 disposed between the second extension electrode 241and the second-type conductivity semiconductor layer 333. In anotherembodiment, the light-emitting device 300 can comprise an ohmic contactlayer 362 disposed between the conductive layer 281 of the firstexternal electrode structure 28 and the second-type conductivitysemiconductor layer 333, and/or between the conductive layer 281 of thesecond external electrode structure 38 and the second-type conductivitysemiconductor layer 333. The ohmic contact layers 222, 242 have theshape as substantially the same as the first and second extensionelectrodes 221, 241, respectively. By virtue of the ohmic contact layers222, 242, 362, a contact resistance between the extension electrode andthe second-type conductivity semiconductor layer 333 and a contactresistance between the conductive layer 281 and the second-typeconductivity semiconductor layer 333 can be reduced.

As shown in FIG. 5B, the light-emitting device 300 comprises a lowerelectrode 37 formed on the substrate 10. The lower electrode 37 and thefirst external electrode structure 28 (or the second external electrodestructure 38) are formed on opposite sides of the substrate 10, therebyforming the light-emitting device 300 with a vertical-type. In addition,since the first-type conductivity semiconductor layer 331 of the firstsemiconductor structure 22 and the first-type conductivity semiconductorlayer 331 of the second semiconductor structure 24 are physicallyconnected with each other, the lower electrode 37 can electricallyconnect with the first-type conductivity semiconductor layer 331 of thefirst semiconductor structure 22 and with the first-type conductivitysemiconductor layer 331 of the second semiconductor structure 24 suchthat the first semiconductor structure 22 and the second semiconductorstructure 24 can be synchronously driven when in operation. Thesubstrate 10 is a conductive substrate and comprises a semiconductormaterial or a metal material.

As shown in FIG. 5A, the first external electrode structure 28 of theelectrode area can function as a first electrode set cooperated with thelower electrode 37 for receiving a first current to form a currentpassage therebetween such that the first semiconductor structure 22 isdriven to emit the first light with a first illumination; the secondexternal electrode structure 38 different from the first electrode setcan function as a second electrode set for receiving a second current todrive the second semiconductor structure 24 to emit the second lightwith a second illumination. The first illumination and the secondillumination can be adjustable by the first current and the secondcurrent, or by a size of the first semiconductor structure 22 and thesecond semiconductor structure 24, for example, the area of the activelayer of the first semiconductor structure 22 and the active layer ofsecond semiconductor structure 24. When the area of the active layer ofthe first semiconductor structure 22 is smaller than the area of theactive layer of second semiconductor structure 24, and a value of thefirst current is equal to that of the second current (the currentdensity of the first semiconductor structure 22 is greater than that ofthe second semiconductor structure 24), the first illumination isgreater than the second illumination. When the area of the active layerof the first semiconductor structure 22 is equal to the area of theactive layer of second semiconductor structure 24 and a value of thefirst current is greater than that of the second current (the currentdensity of the first semiconductor structure 22 is greater than that ofthe second semiconductor structure 24), the first illumination isgreater than the second illumination.

The first electrode set and the second electrode set can separately andsimultaneously receive a current. As shown in FIG. 5A, when only thefirst electrode set, i.e. the first external electrode structure 28receives the first current, the first semiconductor structure 22 isdriven to emit the first light. As shown in FIG. 6, when only the secondelectrode set, i.e. the second external electrode structure 38 receivesthe second current, the second semiconductor structure 24 is driven toemit the second light. As shown in FIG. 7, when the first electrode andthe second electrode set, i.e. the first external electrode structure 28and the second external electrode structure 38 separately receive thefirst current and the second current at the same time, the firstsemiconductor structure 22 and the second semiconductor structure 24 aredriven to simultaneously emit the first light and the second light.

FIGS. 8 through 11 disclose a light-emitting device 400 in accordancewith the fourth embodiment of the present disclosure. FIG. 8 shows a topview of a light-emitting device in accordance with the fourth embodimentof the present disclosure. FIG. 9 is a cross-sectional view along anA-A′ line shown in FIG. 8 after a step of roughing. FIG. 10 is across-sectional view along an A-A′ line shown in FIG. 8 before the stepof roughing. FIG. 11 is a cross-sectional view along a B-B′ line shownin FIG. 8. The light-emitting device 400 has the similar structure withthe first embodiment of the light-emitting device 100. The difference isthat the light-emitting device 400 further comprises a firstsemiconductor layer 30, a second semiconductor layer 14, and a thirdsemiconductor layer 31. The first semiconductor layer 30 is between thefirst electrode 16 and the light-emitting stack 13. The secondsemiconductor layer 14 is between the first electrode 16 and the firstsemiconductor layer 30. The third semiconductor layer 31 is between thebonding layer 11 and the light-emitting stack 13. Referring to FIG. 10,after forming the light-absorbing layer 18 on the second semiconductorlayer 14, a part of the second semiconductor layer 14 is not covered bythe light-absorbing layer 18 and the first electrode 16. Thus the partis exposed. A roughing step is performed to remove the exposed part ofthe second semiconductor layer 14 so as to rough a part of a top surfaceof the first semiconductor layer 30. After the roughing step, thelight-emitting device 400 as shown in FIG. 9 is obtained, wherein thefirst semiconductor layer 30 comprises substantially the same surfacestructure as that of the second-type conductivity semiconductor layer133 in the foregoing embodiment as shown in FIG. 2. In the presentembodiment, the first semiconductor layer 30 has a side wall 301 and atop surface. The top surface comprises a first region 302 and a secondregion 303. The second region 303 is defined by the light-absorbinglayer 18 formed on the first region 302, which means the first region302 surrounds the second region 303. The outer segment 162 of the firstelectrode 16 on the first region 302 surrounds the second region 303.The inner segment 161 of the first electrode 16 is formed on a portionof the second region 303 without covering the entire second region 303.As a result, a part of the first semiconductor layer 30 is exposed suchthat the light emitted from the active layer 132 can pass outside thelight-emitting device 100.

In the present embodiment, the first semiconductor layer 30 has amaximum thickness greater than a thickness of the second-typeconductivity semiconductor layer 133. In the present embodiment, thefirst semiconductor layer 30 has a maximum thickness determined fromfirst region 302 to the bottom of the first semiconductor layer 30. Inone embodiment, the maximum thickness of the first semiconductor layer30 is not less than 500 nm, and preferably, not less than 1000 nm, andmore preferably, between 1500 and 4000 nm both inclusive for improvingcurrent spreading through the light-emitting stack 13 and/or improvingthe extraction efficiency. The first semiconductor layer 30 issubstantially transparent to the light emitted from the active layer.

In one embodiment, the first semiconductor layer 30 has a conductivitytype the same as that of the second-type conductivity semiconductorlayer 133. In one embodiment, the first semiconductor layer 30 is ann-type semiconductor. The first semiconductor layer 30 has a dopingconcentration of a dopant greater than that of the second-typeconductivity semiconductor layer 133 for improving current spreadingthrough the light-emitting stack 13. In one embodiment, the dopingconcentration of the dopant of the first semiconductor layer 30 is notless than 1×10¹⁷/cm³, and preferably, between 5×10¹⁷/cm³ and 5×10¹⁸/cm³both inclusive. The first semiconductor layer 30 has an energy gap lessthan that of the second-type conductivity semiconductor layer 133. Inone embodiment, the first semiconductor layer 30 comprises a Group III-Vsemiconductor material, such as (Al_(y)Ga_((1-y)))_(1-x)In_(x)P, wherein0≦x≦1, 0≦y≦1 or Al_(x)Ga_((1-x))As, wherein 0≦x≦1. In one embodiment,the dopant can be an n-type dopant or a p-type dopant. In oneembodiment, the n-type dopant is Te, or Si. The p-type dopant is C orMg.

After the roughing step, the second semiconductor layer 14 has a patternsubstantially the same as the pattern of the first electrode 16. Asshown in FIG. 9, a part of the second semiconductor layer 14 is betweenthe ohmic contact layer 15 and the first semiconductor layer 30, and theother part of the second semiconductor layer 14 is between the firstsemiconductor layer 30 and the outer segment 162, and specifically,between the first region 302 of the first semiconductor layer 30 and theouter segment 162. As a result, the part of the second semiconductorlayer 14 between the first semiconductor layer 30 and the outer segment162 is directly in contact with the outer segment 162. Specifically, anouter edge of the second semiconductor layer 14 and the side wall 301 ofthe first semiconductor layer 30 are substantially coplanar. Inaddition, as shown in FIG. 9, the second portion of the light-absorbinglayer 18 overlaps a first part of the second semiconductor layer 14, andthe ohmic contact layer 15 overlaps a second part of the secondsemiconductor layer 14 without overlapping the first part of the secondsemiconductor layer 14. Specifically, the first electrode 16 is directlyin contact with the ohmic contact layer 15 and the second semiconductorlayer 14 both. More specifically, referring to FIG. 11, the outersegment 162 of the first electrode 16 and the a plurality of extendingsegments 163 are directly in contact with the second semiconductor layer14, and the inner segment 161 of the first electrode 16 is directly incontact with ohmic contact layer 15. In the present embodiment, thesecond semiconductor layer 14 comprises a Group III-V semiconductormaterial. Preferably, the second semiconductor layer 14 comprises aGroup III-V semiconductor material comprising an element different fromthat of the ohmic contact layer 15, and the element is the same as oneof the elements of the first semiconductor layer 30. The secondsemiconductor layer 14 is for lowering the difference between twodifferent material systems, such as lowering the difference between thematerial of the first semiconductor layer 30 and the material of theohmic contact layer 15. Preferably, the second semiconductor layer 14comprises a Group III-V semiconductor material that is devoid of Al soas to prevent or decrease the formation of byproduct such as nativeoxide; thus improving the adhesion between the second semiconductorlayer 14 and the outer segment 162. In one embodiment, the secondsemiconductor layer 14 comprises In_(a)Ga_(1-a)P, wherein 0≦a≦1, theohmic contact layer 15 comprises Al_(b)Ga_((1-b))As, wherein 0≦b≦1, andthe first semiconductor layer 30 comprises a(Al_(y)Ga_((1-y)))_(1-x)In_(x)P, wherein 0≦x≦1, 0≦y≦1.

In one embodiment, the second semiconductor layer 14 has a dopingconcentration of a dopant less than a doping concentration of a dopantof the ohmic contact layer 15. Preferably, a ratio of the dopingconcentration of the ohmic contact layer 15 to the doping concentrationof the second semiconductor layer 14 is not less than 2, and preferably,between 5 and 15 both inclusive, so as to prevent or decrease thecurrent directly flowing through the part of the second semiconductorlayer 14 between the first semiconductor layer 30 and the outer segment162 and to increase the amount of current flowing through the ohmiccontact layer 15. As a result, the output power of light is improved dueto a higher current density in the second region 303, which is a mainlight extraction area. In one embodiment, the doping concentration ofthe dopant of the second semiconductor layer 14 is not greater than1×10¹⁸/cm³, preferably, not greater than 9×10¹⁷/cm³, and morepreferably, between 1×10¹⁷/cm³ and 7×10¹⁷/cm³ both inclusive. In oneembodiment, the dopant can be an n-type dopant or a p-type dopant. Inone embodiment, the n-type dopant is Te, or Si. The p-type dopant is Cor Mg. In one embodiment, the second semiconductor layer 14 has athickness less than the maximum thickness of the first semiconductorlayer 30, and preferably, less than a thickness of the ohmic contactlayer 15. In one embodiment, the second semiconductor layer 14 has athickness not less than 5 nm, and preferably between 5 nm and 50 nm bothinclusive.

In one embodiment, the third semiconductor layer 31 has a thicknessgreater than a thickness of the first-type conductivity semiconductorlayer 131. In one embodiment, the third semiconductor layer 31 has amaximum thickness not less than 500 nm, and preferably, not less than1000 nm, and more preferably, between 1500 and 4000 nm. In addition, thethird semiconductor layer 31 has a thickness less than the maximumthickness of the first semiconductor layer 30. The third semiconductorlayer 31 has a conductivity type the same as that of the first-typeconductivity semiconductor layer 131. In one embodiment, the thirdsemiconductor layer 31 is a p-type semiconductor. The thirdsemiconductor layer 31 has a doping concentration of a dopant greaterthan that of the first-type conductivity semiconductor layer 131 forimproving current spreading through the light-emitting stack 13. In oneembodiment, the doping concentration of the dopant of the thirdsemiconductor layer 31 is not less than 10¹⁷/cm³, and preferably,between 5×10¹⁷/cm³ and 5×10¹⁸/cm³ both inclusive. The thirdsemiconductor layer 31 has an energy gap less than that of thefirst-type conductivity semiconductor layer 131. In one embodiment, thethird semiconductor layer 31 comprises a Group III-V semiconductormaterial, such as (Al_(y)Ga_((1-y)))_(1-x)In_(x)P, wherein 0≦x≦1, 0≦y≦1or Al_(x)Ga_((1-x))As, wherein 0≦x≦1. In one embodiment, the dopant canbe an n-type dopant or a p-type dopant. In one embodiment, the n-typedopant is Te, or Si. The p-type dopant is C or Mg.

FIG. 12 disclose a light-emitting device 500 in accordance with thefifth embodiment of the present disclosure. The top view of thelight-emitting device 500 is substantially the same as the top viewshown in FIG. 8. FIG. 12 is a cross-sectional view along an A-A′ lineshown in FIG. 8. The light-emitting device 500 has the similar structurewith the fourth embodiment of the light-emitting device 400. Thedifference is that the second semiconductor layer 14 has a patternsubstantially the same as the pattern of the ohmic contact layer 15 inthe present embodiment. As shown in FIG. 8 and FIG. 12, the ohmiccontact layer 15 and the second semiconductor layer 14 each are annularaccording to the fifth embodiment, and the outer segment 162 is directlyin contact with the first semiconductor layer 30, specifically, isdirectly in contact with the first region 302 of the first semiconductorlayer 30. The first electrode 16 is directly in contact with the ohmiccontact layer 15 and the first semiconductor layer 30 both. Morespecifically, the outer segment 162 of the first electrode 16 isdirectly in contact with the first semiconductor layer 30, and the innersegment 161 of the first electrode 16 is directly in contact with ohmiccontact layer 15. In the present embodiment, the first semiconductorlayer 30 comprises a Group III-V semiconductor material comprising acontent of Al, wherein the content of Al is less than a content of Al inthe second-type conductivity semiconductor layer 133 so as to ordecrease the formation of byproduct such as native oxide; thus improvingthe adhesion between the first semiconductor layer 30 and the outersegment 162. Preferably, the first semiconductor layer 30 comprises(Al_(y)Ga_((1-y)))_(1-x)In_(x)P, wherein 0≦x≦1, 0≦y≦0.3 orAl_(x)Ga_((1-x))As, wherein 0≦x≦0.3, for improving the adhesion betweenthe first semiconductor layer 30 and the outer segment 162.

In the present embodiment, the doping concentration of the dopant of thesecond semiconductor layer 14 is not limited to be not greater than1×10¹⁸/cm³. In accordance with a further embodiment of the presentdisclosure, the structures in the embodiments of the present disclosurecan be combined or changed. For example, the light-emitting device asshown in FIGS. 5A and 5B comprises the first semiconductor layer 30,second semiconductor layer 14 and/or the third semiconductor layer 31.

The foregoing description has been directed to the specific embodimentsof this invention. It will be apparent to those having ordinary skill inthe art that the foregoing embodiments alone or combinations thereofshall be a part of the present disclosure, and other alternatives andmodifications can be made to the devices in accordance with the presentdisclosure without departing from the scope or spirit of the disclosure.In view of the foregoing, it is intended that the present disclosurecovers combinations, modifications and variations of this disclosureprovided they fall within the scope of the following claims and theirequivalents.

What is claimed is:
 1. An light-emitting device, comprising: a light-emitting stack; a first semiconductor layer on the light-emitting stack; a first electrode formed on the first semiconductor layer and comprising an inner segment, an outer segment, and a plurality of extending segments electrically connecting the inner segment with the outer segment.
 2. The light-emitting device of claim 1, further comprising a second semiconductor layer between the first semiconductor layer and the first electrode, wherein the second semiconductor layer has a thickness less than a maximum thickness of the first semiconductor layer.
 3. The light-emitting device of claim 2, wherein the first electrode is directly in contact with the second semiconductor layer.
 4. The light-emitting device of claim 3, wherein the second semiconductor layer comprises a Group III-V semiconductor material devoid of Al.
 5. The light-emitting device of claim 3, wherein the outer segment of the first electrode is directly in contact with the second semiconductor layer.
 6. The light-emitting device of claim 5, wherein the second semiconductor layer has a doping concentration of a dopant not greater than 1×10¹⁸/cm³.
 7. The light-emitting device of claim 2, further comprising an ohmic contact layer between the second semiconductor layer and the first electrode.
 8. The light-emitting device of claim 7, wherein the second semiconductor layer and the ohmic contact layer each have a doping concentration, and a ratio of the doping concentration of the ohmic contact layer to the doping concentration of the second semiconductor layer is not less than
 2. 9. The light-emitting device of claim 7, wherein the first electrode is directly in contact with the first semiconductor layer.
 10. The light-emitting device of claim 9, wherein the outer segment of the first electrode is directly in contact with the first semiconductor layer.
 11. The light-emitting device of claim 10, wherein the inner segment of the first electrode is directly in contact with the ohmic contact layer
 12. The light-emitting device of claim 9, wherein the light-emitting stack comprises a first-type conductivity semiconductor layer, a second-type conductivity semiconductor layer, and an active layer sandwiched between the first-type and second-type conductivity semiconductor layers, the first semiconductor layer is between the second-type conductivity semiconductor layer and the first electrode, and the first semiconductor layer and the second-type conductivity semiconductor layer each comprises a Group III-V semiconductor material comprising a content of Al, wherein the content of Al of the first semiconductor layer is less than the content of Al of the second-type conductivity semiconductor layer.
 13. The light-emitting device of claim 9, wherein the first semiconductor layer comprises (Al_(y)Ga_((1-y)))_(1-x)In_(x)P, wherein 0≦x≦1, 0≦y≦0.3 or Al_(z)Ga_((1-z))As, wherein 0≦z≦0.3.
 14. The light-emitting device of claim 2, wherein the second semiconductor layer comprises an outer edge, and the outer edge and a side wall of the first semiconductor layer are substantially coplanar.
 15. The light-emitting device of claim 1, further comprising a light-absorbing layer on the first semiconductor layer, wherein the first semiconductor layer has a side wall, and the light-absorbing layer covers the side wall.
 16. The light-emitting device of claim 15, further comprising a reflective layer under the light-emitting stack.
 17. The light-emitting device of claim 16, wherein in a cross-sectional view of the light-emitting device, the reflective layer is not vertically overlapped with the light-absorbing layer.
 18. The light-emitting device of claim 15, wherein the first electrode comprises metal or metal alloy.
 19. The light-emitting device of claim 18, wherein the light-absorbing layer comprises titanium (Ti), chromium (Cr), nickels (Ni), Au, or combinations thereof.
 20. The light-emitting device of claim 15, wherein the first semiconductor layer comprises a top surface comprising a first region and a second region, the light-absorbing layer is on the first region and does not cover the second region, and a part of the second region is roughened. 